Autoinjector (AI) devices are held against the body while an injection needle pierces the skin to administer a drug product. While gripping the AI, the user applies a downward movement against the skin that activates the AI. The user then presses a button to cause the needle to inject and the stopper to move the drug downward into the skin.
During needle insertion and plunger movement, the interface/surface area between the user's skin and the AI's physical area touching the skin (and encompassing the needle) must remain in place to avoid AI and/or needle slippage or movement on the surface of the skin. This must occur to enable a full drug dose delivery, to avoid drug leakage on the skin's surface, and most importantly, to avoid user injury from a bent or broken needle during the injection process. Additionally, for user comfort, it is advised that the injection site's skin area, and directly under the AI, be kept taut to facilitate the injection procedure.
Today's AI procedures advise users to stretch or pinch the skin at the injection site with one hand and to maintain that stretch or pinch while placing the AI over the same area. With the AI in place, the user applies a downward force on the site area to activate or unlock the device. While keeping the skin stretched or pinched with one hand and the AI gripped in position with the other, the user must then use the thumb of the hand holding the AI to depress a button located at the top of the AI, thereby, activating needle and plunger downward movement to inject the drug. After the injection is completed, the needle may be retracted from the skin and the user lifts off the device.
During the act of placing and activating the AI onto the site, users have been observed to: 1) lose concentration, letting go of the stretched or pinched skin, and attempting to maneuver the AI into place; 2) let go of the stretched or pinched skin in order to grip the AI with two hands due to their lack of physical hand strength or dexterity; and 3) lift the device off too soon before the injection is complete. Further, the use of AIs can be a significant challenge for seniors or finger function compromised users and consequently, treatment can be hindered.
Hence, there are multiple considerations for the front wall at the injection end of the AI. One such consideration is the AI's ability to stretch skin. The user is not expected to stretch the skin while injecting with the AI, therefore, it would be very beneficial to have a feature on the AI that will provide this function. Another consideration is to provide the AI with a feature that improves the stability of the AI, so that it remains approximately perpendicular to the body during injection, thereby allowing the user to operate the AI with one hand. Still another consideration is that some commercial AIs require the application of an axial force to a trigger release mechanism on the front wall of the AI where it contacts the user's skin. Some body types have lower surface tension and resistance to the required activation force thereby causing the AI to press against the skin and deflect into the body a significant amount. Some patients do not apply the required activation force thereby not allowing the AI to arm and be ready to inject. Some commercial AIs have a shield trigger and activation button which must be pressed to arm and initiate delivery. Other commercial AIs only require a shield trigger to be pressed to arm and initiate delivery.
Accordingly, methods are needed which solve the placement, activation, and ergonomic design issues of conventional AIs.